The goals of this research project are to elucidate some of the biochemical mechanisms by which an RNA-enveloped virus is replicated and released from its animal cell host. In the initial research proposed, tissue culture cells infected with Sindbis virus will provide the experimental system for the isolation and study of those enzymes required for processing viral structural proteins from larger molecular weight precursor polypeptide chains that appear as the initial viral gene products. Altered defective forms of Sindbis virus, different host cell lines, different growth conditions, and metabolic inhibitors are to be used for accumulating, isolating, and identifying precursors of viral structural proteins. These materials, in turn, can serve as substrates for seeking those specific proteolytic enzymes required in viral development. Results of such studies should reveal the extent to which host cell enzymes control viral growth, the role that virus may play in modifying normal host cell enzymes, and the possible function that these enzymes may have in animal cell growth and metabolism. Part of the maturation process in production of an RNA enveloped virus appears to be proteolytic cleavages of viral glycoproteins that form part of the host cell plasma membrane. There is increasing evidence that alteration of glycoproteins on cell surfaces may be an important event in the regulation of animal cell growth and metabolism. Thus, the research proposed here on modifications of viral membrane proteins should not only reveal viral-cell relationships but may also provide a valuable model system for probing regulation of normal cell growth.